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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Miguel Dahl on August 21, 2018, 02:09:45 pm

This might be a stupid question, but I'm curious about the difference.

If running a signal line to several active speakers, where one of them is powered from a different outlet with a different ground potential. Is there a difference in using a galvanic isolation between all three XLR-pins and just "lifting" pin 1? on the signal feeding the speaker on a different ground potential relative to the ground potential to where the signal originates from?

This might be a stupid question, but I'm curious about the difference.

If running a signal line to several active speakers, where one of them is powered from a different outlet with a different ground potential. Is there a difference in using a galvanic isolation between all three XLR-pins and just "lifting" pin 1? on the signal feeding the speaker on a different ground potential relative to the ground potential to where the signal originates from?

Depends on the input. if it is transformer isolated no problem. It is much more likely that you will need to have an isolation transformer in the line.

Thanks, but I feel it didn't answer my question regarding what "answer I seek", the difference between a 3p iso and just a pin one iso.

A transformer is a 2 pin iso. Lifting pin 1 just disconnects the ground but if your equipment is NOT transformer isolated, pin 1 does not really isolate it, particularly if it is and electrally balanced I/O.

This might be a stupid question, but I'm curious about the difference.

perhaps... do you have a problem?

Quote

If running a signal line to several active speakers, where one of them is powered from a different outlet with a different ground potential. Is there a difference in using a galvanic isolation between all three XLR-pins and just "lifting" pin 1? on the signal feeding the speaker on a different ground potential relative to the ground potential to where the signal originates from?

If the active speakers have a well designed input there will be no difference, if they don't the answer is not to float the ground (pin 1), but maybe see if the speakers float in the canal out back.

perhaps... do you have a problem? If the active speakers have a well designed input there will be no difference, if they don't the answer is not to float the ground (pin 1), but maybe see if the speakers float in the canal out back.

JR

OK, let's assume that we've got balanced in/out, and they are well-isolated, so there's no impact on the audio. If there is voltage potential between the two grounds -- "pin 1" -- could you conceivably get a current flowing on the shield? What is the likely current? Could it be high enough to lead to undesirable heating of the shield?

OK, let's assume that we've got balanced in/out, and they are well-isolated, so there's no impact on the audio. If there is voltage potential between the two grounds -- "pin 1" -- could you conceivably get a current flowing on the shield? What is the likely current? Could it be high enough to lead to undesirable heating of the shield?

sure... mike probably has pictures of melted stuff over in the power forum from rogue ground currents.

OK, let's assume that we've got balanced in/out, and they are well-isolated, so there's no impact on the audio. If there is voltage potential between the two grounds -- "pin 1" -- could you conceivably get a current flowing on the shield? What is the likely current? Could it be high enough to lead to undesirable heating of the shield?

My point being that there may be reasons other than sound quality to isolate or lift pin 1.

sure... mike probably has pictures of melted stuff over in the power forum from rogue ground currents.

JR

Indeed, this Sticky (https://r.tapatalk.com/shareLink?share_fid=32177&share_tid=137760&url=http%3A%2F%2Fforums%2Eprosoundweb%2Ecom%2Findex%2Ephp%3Ftopic%3D137760&share_type=t) is all about that, due to a RPBG and the snake wiring was the fuse.

I'm probably repeating myself but UL performs a ground bonding test on any external product connection labelled as ground, to carry something like 50A fault current with single digit voltage rise. That wire melting is obviously a failure, but that audio jack may not have been labelled "ground". The intent is to protect humans irrespective of where the fault occured, and trip the breaker.

I'm probably repeating myself but UL performs a ground bonding test on any external product connection labelled as ground, to carry something like 50A fault current with single digit voltage rise. That wire melting is obviously a failure, but that audio jack may not have been labelled "ground". The intent is to protect humans irrespective of where the fault occured, and trip the breaker.

I had to redesign a PCB inside a small install mixer/amp product when the UL ground bond test completely evaporated a PCB trace off the circuit board. I had the option of relabelling the audio termination 0V instead of "ground", but did the right thing and passed the test with a new fatter ground trace on the PCB.

I had to redesign a PCB inside a small install mixer/amp product when the UL ground bond test completely evaporated a PCB trace off the circuit board. I had the option of relabelling the audio termination 0V instead of "ground", but did the right thing and passed the test with a new fatter ground trace on the PCB.

Ground bond test has to pass several tens of amps with low single digit voltage drop.

The first commercial ground bond tester I found on google provides 10A to 30A test current.

Quote from: ESTGUIDE.P65

Ground BondA ground bond test verifies integrity of theground path by applying a high current, lowvoltage source to the ground path circuit,typically a 25 or 30 A current.This test is similar to the ground continuitytest with the additional benefit of verifyinghow a product will perform under actual faultconditions.When a ground fault occurs, current startsto flow through the ground circuit. If thecurrent-carrying capacity is high enoughand the circuit resistance low enough, thesystem operates properly and the user isprotected from shock.If, however, the ground circuit cannot carryenough current or has too high an electricalresistance, the circuit breaker may not tripor the fuse may not blow. If this occurs,voltage can build up to a point where currentwill flow through the userís body insteadof the ground circuit.

Ground bond test has to pass several tens of amps with low single digit voltage drop.

The first commercial ground bond tester I found on google provides 10A to 30A test current.

I try not to be too pedantic but ground safety is important.

JR

I'm with JR on this one. Remember, this isn't continuous current, but it needs to be long enough in duration to trip a circuit breaker. That's the primary job of the EGC (Equipment Grounding Conductor). The NEC could care less about reducing hum in your sound system. They just don't want anything to have a elevated voltage due to a line-to-chassis short.